Then \(W_+\)  has the following stationary representation (see e.g. [1]}, [2]}):
\(W_+=\mathop {\mathrm {Id}}\nolimits -\frac{2}{\pi i}\int _0^\infty \lambda ^3 R_V^+(\lambda ^4)V\left(R_0^+(\lambda ^4)-R_0^-(\lambda ^4)\right)d\lambda .\) 
